Arvicolini (Rodentia) from the Irvingtonian of north-central Kansas, USA

The Fiene local fauna, located in north-central Kansas, is one of the few Pleistocene microfaunas in the state located outside the Meade Basin. The fauna includes a variety of vertebrate taxa, including a small but diverse assemblage of arvicoline rodents. Seven morphotypes of the first lower molar are recognizable among the specimens assignable to Arvicolini. These include a form with five closed triangles assigned to Microtus sp., three morphotypes with four closed triangles assigned to M. paroperarius, and three morphotypes with three closed triangles assigned to M. llanensis, M. meadensis, and Allophaiomys sp. The co-occurrence of these forms supports an Irvingtonian age for the site, and constitutes a relatively rare taxonomic assemblage for the Great Plains. The Fiene thus may prove important for testing future questions of provinciality in arvicoline biochronology and faunal dynamics. Recent phylogenetic hypotheses, based largely on molecular sequence data, have complicated the interpretation of isolated fossil teeth by proposing the extant species of North American Microtus are monophyletic and that taxa characterized by three closed triangles on the m1 evolved independently from five-triangled forms. The ability of fossil assemblages, such as Fiene, to meaningfully inform broad questions of arvicoline evolution requires that paleontologists improve their ability to place isolated teeth into this expanded phylogenetic context. Rather than depressing paleontological study, this requirement hopefully will be embraced as an opportunity to expand research on the arvicoline dentition.